The present invention relates to communications network and local area networks and, more particularly, to the method and associated apparatus for operating a local area communications network so as to permit a plurality of nodes to transmit and receive voice, video, and other forms of real-time traffic between one another along with normal computer communications according to the method comprising the steps of, disposing a communications medium along a path between the nodes; employing a plurality of interfacing units to operably connect respective ones of the nodes to the communications medium; inputting real-time communications traffic from a transmitting node into an elastic FIFO transmitting buffer; removing stored traffic from the transmitting buffer in fixed length packets and transmitting the packets sequentially onto the communications medium; inputting the packets sequentially from the communications medium into an elastic FIFO receiving buffer at a receiving node; and, removing the packets from the receiving buffer and transmitting them to the associated receiving node in contiguous form to reconstruct the original real-time transmission. More specifically, the communications medium is a token passing ring where a token bit sequence is transmitted along a ring communications medium to indicate the point where a packet can be placed onto the ring and the method additionally including the steps of, at each transmitting node, preceeding each token bit sequence with an idle period of non-transmission; and, at each receiving node, sensing the idle period and using the bits of the token bit sequence to establish and synchronize to the clock of the packet following thereafter whereby clock information relative to the packets is conveyed across boundaries of the network. Additionally, the preferred method includes the steps of, monitoring the average size of the receiving buffer; slowing the filling of the receiving buffer when the average size is increasing; and, increasing the filling of the receiving buffer when the average size is decreasing whereby the average size is maintained in a stable state and the receiving buffer is prevented from being totally emptied or from overflowing.
Network communication systems have gained great popularity recently because of the many advantages they offer. For example, as shown in simplified form in FIG. 1, it is common to have a plurality of computers 10 interconnected by a communications network 12 over which messages 14 can be passed from computer to computer. Fiber optics is another fairly recent technological achievement that has gained rapid acceptance for its benefits--particularly in voice quality communications where a quiet communications channel free from electromagnetic interference (EMI), and the like, (which normally accompany wire systems) is desired or required. In the typical voice fiber optic communications system as depicted in FIG. 2, the telephone 16 (or modem, etc.) on each end is connected to the fiber optic bundle 18 by bi-directional coupling devices 20 which turn an electrical signal from the telephone 16 into a light signal for transmission over the fiber optic bundle 18 and back to an electrical signal at the opposite end. Typical voice communication is continuous as opposed to the discrete messages 14 of the computer network of FIG. 1; that is, once a connection has been established between the two telephones 16, it is available and open for communication--whether or not any actual communication is taking place. Thus, if one wishes to combine both computer message transmission and voice communications over a common communications channel as depicted in FIG. 3, the voice messages must be packetized, i.e. broken up into segments such as the computer messages 14 (with which they share the channel) which are then sent like any of the messages 14 and then "reconstructed" on the receiving end into a contiguous message stream. Such packetization of voice communications is known in the art and happens all the time in satellite communications systems.
The availability of low-cost high-capacity fiber optic communications has recently provided new impetus for practical integrated service data networks (ISDN), i.e. networks providing various communications on a single shared channel. Many different protocol strategies have been proposed over the past few years for combining data, voice, video, and other forms of real-time traffic onto one local area (10 km) network (LAN). These range from highly synchronous protocols dedicating isolated channels for the real-time service via TDM, slotted transmission frames, or Wavelength Division Multiplexing (WDM) to complex reservation bit schemes using a single common packet channel. Of the latter, deterministic protocols such as token rings, token buses, unidirectional buses, or modified CSMA/CD buses with deterministic contention resolution are suitable. Most real-time services, such as voice or video, require bandwidth significantly beyond the few Mbit/s capacity of most of these LANs, however, and furthermore, few of these protocols will provide high efficiency at higher data rates should technology permit further growth in the future. The proposed Fiber (Optic) Distributed Data Interface (FDDI) standard, which is based on a streamlined token ring protocol and optimized for 1.3-um fiber optic technology, however, is seen as one promising candidate for real-time networks. With 200 Mbit/s of capacity and a highly deterministic dual-counter-rotating token ring topology, FDDI possesses enough bandwidth to support up to 800 voice channels or perhaps 1-2 digitized video channels. One problem with transporting voice or video traffic over FDDI, however, is that the network and interface are asynchronous, thereby preventing timing information from passing across the network boundaries. While a synchronous version of FDDI may ultimately emerge, what is required at this time is an alternate method of transmitting synchronous voice traffic over an asynchronous packet switched FDDI--in effect creating a virtual T1 channel.
Wherefore, it is an object of the present invention to provide an alternate method of transmitting synchronous voice traffic over an asynchronous packet switched FDDI network based on double buffering real-time data at both the transmitting and receiving ends of the packet switched network to, in effect, create a virtual T1 channel.
It is another object of this invention to provide an alternate method of transmitting synchronous voice traffic over an asynchronous packet switched FDDI network wherein timing information is conveyed across the boundaries between the transmitting and receiving ends of the packet switched network.
Other objects and benefits of the present invention will become apparent from the description which follows hereinafter in conjunction with the drawing figures which accompany it.